Project Summary/Abstract Brugada syndrome is a genetic disorder that increases the risk of sudden cardiac death. While several genetic mutations affecting cardiac ionic channels have been identified in patients with Brugada syndrome, the underlying causes of arrhythmia and sudden cardiac death remain unknown and in debate. It has been hypothesized that combined with the presence of the transient outward potassium current, Ito, these mutations result in spike-and-dome action potential morphologies that can facilitate phase 2 reentry, a possible trigger of arrhythmias that has been demonstrated in experimental studies. However, patients with Brugada syndrome also show fibrosis and fractional ECGs, implying conduction delay may be a primary mechanism as well. Dissecting the mechanisms using experiments or clinical studies alone has a huge challenge due to the complexity of Brugada syndrome, and therefore the goal of this study is to combine biological experiments on cardiac myocytes with mathematical modeling and computer simulation. In silico approaches have the advantage of handling complex systems, particularly when we wish to analyze the behavior of layers of interacting cells in multiple dimensions. Using both experimental and computational approaches, I plan to determine the underlying mechanisms of arrhythmias in Brugada syndrome. Specifically, I will test the hypothesis that under the presence of Ito, Brugada syndrome mutations can result in complex cellular action potential dynamics, which then interact with structural tissue heterogeneities to potentiate arrhythmogenesis. Specific Aim 1 focuses on the mechanisms of complex single-cell action potential dynamics caused by mutations of Brugada syndrome. I will perform and analyze simulations of models of single-cell cardiac ventricular myocytes in order to determine the key features that lead to complex action potential dynamics. Biological experiments using dynamic clamp protocols and optical mapping will validate the simulation results and guide new experiments and simulation studies. Specific Aim 2 focuses on the tissue-scale dynamics caused by mutations of Brugada syndrome. Computer simulations of layers of cells aligned in 1-, 2-, and 3-dimensional arrays under multiple situations will provide evidence to the global behavior of cardiac tissue and pinpoint the effects of key factors, such as cell-to-cell coupling, tissue heterogeneities, and/or cellular action potential dynamics, that promote arrhythmias and sudden cardiac death.